Commit 50f05448982b5fafd9d9a7783b639dd145090a0d to os-client-config
removed the default values in the _defaults dict. This makes any
call to cloud_config.set_default() before initializing the dict
fail.
The fix changes the way the auth_type default is overriden, by
doing it when cloud_config.OpenStackConfig() is executed.
Change-Id: If37d3ba303f01d4c77fd7c15a3cde9634534b64a
Closes-bug: #1473921